Narendra Modi arrived in Lahore on a surprise stopover Friday in the first visit by an Indian prime minister to Pakistan since 2004.
His plane landed at the Allama Iqbal International Airport in the eastern city. Modi was in Kabul earlier Friday where he met Afghan President Ashraf Ghani and addressed parliament.
This is also Modi's first visit to New Delhi's rival neighbour since being elected last year.
India's Atal Bihari Vajpayee visited Pakistan in 2004.
"Looking forward to meeting PM Nawaz Sharif in Lahore today afternoon, where I will drop by on my way back to Delhi," Modi wrote earlier on Twitter.
Modi earlier spoke with Sharif over the phone, who turned 66 on Friday, and wished him a happy birthday.
He was scheduled to visit Pakistan for a regional summit next year.
"That's like a statesman. Padosi se aise hi rishte hone chahiyen [Ties with neighbours should be like this]," Indian Foreign Minister Sushma Swaraj wrote on Twitter in Hindi.
"We have been informed by the Indian High Commission that Prime Minister Narendra Modi would stop over in Lahore to meet our prime minister today. Details are being worked out," confirmed Pakistan's Foreign Ministry spokesman Qazi Khalilullah.
Another Pakistani official said Modi will be received by Sharif, and will stay in the country for about two hours.
India and Pakistan have had troubled ties in past decades over border disputes and terrorism accusations. The South Asian neighbours this month agreed to resume stalled peace talks.
While Indian media said the meeting was significant and showed that the Modi government's diplomacy had a new radical approach to ties with Pakistan, the main opposition Congress party criticized the secrecy surrounding the visit.
"You do not conduct diplomacy at the apex level in such a cavalier manner," Congress spokesman Manish Tiwari told reporters, adding that India Pakistan ties were of a most "complex and complicated" nature.
Modi and Sharif last met in Paris on the margins of the climate summit in November.
That impromptu meeting reportedly laid the ground for talks between the national security advisors of the countries. Those talks were also held secretly in Bangkok on December 6. Swaraj visited Islamabad for a conference on Afghanistan days later.